If you’re going to drive, you have to follow the rules, and most of us are familiar with the basics. However, there are a handful of lesser-known road rules. Maybe you learned them in driver’s ed, but forgot them, because they’re not as important as, say, stopping at a red light. Still, they’ll help you navigate efficiently and communicate silently with other drivers.

Exit Panel Placement Warns You of a Left Exit

My dad recently clued me in on this, but it’s something we’ve covered before, too: if a freeway exit is on the left, you can tell by the sign placement.

Not all left exits are marked this way, though. Some exit panels, right or left, are positioned in the middle, which doesn’t really help you. However, if you come across a left-positioned panel, let it be a heads up—the exit will be on the left.

Exit Numbers Tell You How Far You Have to Go

You’re probably familiar with the function of mile markers, which show you the number of miles ago (or left) where the highway entered your state. According to the Federal Highway Administration, the counting always starts at the south state line for north-south routes and in the west for east-west routes.

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One reader gave us a heads up about distance-based exit numbers, which correspond with these mile markers.

It’s useful info for figuring out where you are and how far you have to go. For example, if you pass Exit 40, you know you’re close to Mile 40. Thus, if you need to get off on Exit 50, you can easily tell you’re 10 miles away.

Highway Numbers Tell You Where You’re Headed

Your highway number is another indication of where you’re headed. Interstate highways follow an odd or even numbering system.

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If the highway has an odd number, it’s traveling north-south and the numbers increase from the West Coast (I-5) to the East Coast (I-95). If the highway is even, it’s traveling east-west, and the numbers should increase from south (I-10) to north (I-94). Of course, sometimes highways veer off in different directions for a while, but as the Federal Highway Administration points out, the rule is based on the overall direction of the highway.

And then there are three-digit interstate highways. The numbers in a three-digit highway generally tell you a few things:

If the first digit is even, the highway usually connects to another interstate at both ends, meaning it’s a loop.

If the first digit is odd, the highway is typically a “spur” route.

The last two numbers usually tell you which interstate the route spurs off from. For example: I-210 in California branches off of I-10. Houston’s I-610 loop branches off of I-10, too.

Again, these rules are typically the case, but there are always a few exceptions. As Snopes points out, I-238 in California doesn’t spur off of Interstate 38, as Interstate 38 doesn’t exist.

Truck Drivers Have Their Own Headlight Code

You probably already know to flicker your high beams at someone who’s driving without theirs on at night to signal to them that they should turn them on. Beyond that, there’s some interesting headlight vocabulary that truckers in particular use to communicate, simply because they drive so much.

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For example, you probably already know that when a truck (or just another car) puts on their blinker to get into your lane, quickly flashing your brights at them says, “go ahead.” If they flash their tail lights (we previously said “tap their brakes” here, this was incorrect) twice, that’s their way of saying, “thank you.” Broken Secrets outlines a few others:

The most common signal is used by cars and trucks in oncoming lanes. They will double-flash their headlights when they just passed a police speed trap that you’re heading toward. While this is very helpful, be sure you know your local laws about this, in some places it is against the law.

More than two consecutive flashes from oncoming traffic signals that there is another type of danger ahead, such as a foreign object on the road and drivers should proceed with caution.

Truck drivers will put their flashing hazard lights on when the highway traffic is coming to an abrupt stop. This signal is fairly common among drivers in Europe, but is only common among truck drivers in North America.

These rules are helpful for truck drivers because it can be tough to maneuver a huge vehicle around a bunch of smaller, speedy cars. However, they come in handy for the rest of us, too. Plus, they’re kind of fun.

Blue Reflectors Are Fire Hydrant Warnings

You’ve probably been in this scenario: you’re looking for parking, you think you see a spot, but nope, it’s a fire hydrant. If you pay attention, the road often gives you a heads up on this, though. Blue reflectors on the road are a sign that there’s a fire hydrant up ahead.

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While this is designed for firefighters, it’s useful for those of us who have trouble parking, too. Similarly, white markers indicate lane markings, yellow markers separate traffic in opposite directions (or mark the left pavement on one-way streets), and if you see red markers, that’s a warning that you’re driving in the wrong direction. Red markers are actually clear, white or yellow when you’re going the right way.

Most of us know and follow the basic rules of the road. There are a lot of rules, though, which means many of the less urgent ones are forgotten. These aren’t as important as others, but they’re still useful nuggets to have on hand.